Objective: To report four new cases of phosphodiesterase 10A (PDE10A) IgG neurological autoimmunity.

Background: PDE10A IgG was recently identified as a biomarker of paraneoplastic neurological disorders, in 7 patients presenting predominantly with movement disorders.[1]

Method: We describe 4 additional patients with PDE10A-IgG neurological autoimmunity. PDE10A-IgG was identified by murine brain tissue indirect immunofluorescence and confirmed by cell-based assay, in 3 sera and 4 CSF samples.

Results: Three patients were female. Median age at onset of symptoms was 61 years (range 53-68). Clinical manifestations included hemichorea with small cell lung cancer (1), parkinsonism and encephalopathy with renal cell carcinoma (1), brainstem and cerebellar syndrome without underlying malignancy (1), and fasciculations with muscle cramps in the context of renal cell carcinoma diagnosis and co-existing serum Ma2 antibodies.  The patient with hemichorea and small cell lung cancer developed symptoms after treatment with immune checkpoint inhibitors, and responded partially to treatment with steroids. Partial response to steroids was also witnessed in the patient with brainstem and cerebellar syndrome, while there was no response to intravenous immunoglobulin treatment for the patient with fasciculations and muscle cramps. Cerebrospinal fluid (CSF) showed inflammatory abnormalities in 2 patients (pleocytosis,1; CSF-unique oligoclonal bands,1).

Conclusion: These 4 cases add to the previous Mayo Clinic series, supporting PDE10A-IgG as a biomarker of paraneoplastic neurological syndromes.  PDE10A-IgG autoimmunity should be considered in the differential diagnosis of patients presenting with subacute movement disorders, particularly in those previously treated with immune checkpoint inhibitors. We suspect that the PDE10A antibodies in the patient with mild peripheral hyperexcitability manifestations are actually biomarkers of the underlying malignancy rather than the neurological syndrome itself.

References: [1] Zekeridou A, Kryzer T, Guo Y, Hassan A, Lennon V, Lucchinetti CF, Pittock S, McKeon A. Phosphodiesterase 10A IgG: A novel biomarker of paraneoplastic neurologic autoimmunity. Neurology. 2019 Aug 20;93(8):e815-e822. doi: 10.1212/WNL.0000000000007971

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MDS Abstracts - https://www.mdsabstracts.org/abstract/movement-disorders-with-phosphodiesterase-10a-igg-autoimmunity/